Stimulus Omission and the Orienting Response

Omission of a stimulus, after its regular presentation has resulted in response habituation, was observed by Sokolov to elicit an orienting response. Although noted some years ago to be crucial in differentiating competing theories of response habituation, strong support for the existence of this phenomenon is lacking in the literature. The present study examined the magnitude of the orienting response to stimulus omission as a function of sex, initial response magnitude, and habituation rate. Response magnitude was significantly greater following stimulus omission than in a control period, and this difference was independent of sex, initial response magnitude, and habituation rate. However, only 22 of the 48 subjects showed greater activity following stimulus omission than in the control period, and 9 showed the reverse. While confirming the existence of the missing-stimulus effect, these results indicate that the phenomenon is relatively fragile when compared with expectations from a reflexive, involuntary stimulus-comparator process as proposed by Sokolov.